This invention relates to an in-cylinder injection gasoline engine and more particularly to a combustion chamber arrangement for such engines.
It has been proposed to employ direct cylinder injection to improve the performance and particularly the fuel economy and exhaust emission control of internal combustion engines. By utilizing direct cylinder injection, it is possible to obtain stratification under some running conditions to allow the engine to run on a leaner than stoichiometric mixture. In this way it is not necessary to provide a homogeneous stoichiometric mixture in the entire combustion chamber to initiate combustion and to develop the required power.
To accomplish this in an open chamber, the fuel injector must inject fuel in a way to form a fuel patch that will be present at the spark gap at the time it is fired. Although this can be easily accomplished if a pre-chamber is employed, it is difficult to achieve this result in an xe2x80x9copen chamberxe2x80x9d. Open chambers are preferred for a variety of reasons including the pumping losses generated by the pre-chamber.
FIGS. 1 and 2 illustrate a typical type of approach that attempts to produce this result in an open chamber. FIG. 1 is a top plan view of a piston used in the arrangement and the associated fuel injector as mounted in the cylinder head. FIG. 2 is a cross sectional view taken along the line 2xe2x80x942 of FIG. 1. As seen in these figures, a piston, indicated generally by the reference numeral 11 reciprocates in a cylinder bore, indicated by the reference numeral 12. The piston 11, cylinder bore 12 and an associated cylinder head surface 13 define the combustion chamber.
The head of the piston 11 is formed with a dome comprised of a pair of angularly related, inclined surfaces 14 and 15 which join a generally flat upper surface 16. A bowl or recess 17 is formed in the piston head and extends through the inclined surface 15 and the. upper flat surface 16. This bowl 17 has a generally curved configuration which extends upwardly and terminates at its inner peripheral edge adjacent a spark plug 18. The spark plug 18 positioned generally on the axis of the cylinder bore 12.
A fuel injector 19 is mounted in the cylinder head surface 13 or cylinder block at one side of the cylinder bore 12. This fuel injector 19 sprays fuel toward and into the piston bowl 17. In addition, a swirl is generated in the combustion chamber as indicated by the arrows A. This swirl is generated by the induction system so as to sweep the injected fuel in a path indicated by the arrow B in the bowl 17 and toward the gap of the spark plug 18. In addition, the inclined surface 14 forms a squish area that drives the air in the direction indicated by the arrows D in FIG. 2. so as to prevent the fuel from escaping from the bowl 17 beyond the outer periphery of the area bounded by the spark plug 18.
An engine of this type may also be provided with a variable valve timing mechanism for varying the valve timing and/or degree of opening of the valves. Thus, the configuration of the combustion chamber and particularly the head surface of the piston 11 must be such as to afford clearance between the valve heads and the piston surfaces under all timing and lift conditions. This results in the formation of a lower than desired compression ratio.
Also, under off idle loads there may be fuel left deposited on the piston bowl 17 after combustion has completed. This increases the problem of hydrocarbon emissions. Furthermore, even though the spark plug 18 is positioned at the center of the combustion chamber, there is a likelihood that fuel may pass beyond the bowl 17 toward the opposite side of the combustion chamber regardless of the swish action indicated by the arrows D. Thus there can be further unburned fuel in the combustion chamber.
Furthermore these conditions increase the likelihood of knocking, even though a low compression ratio has been dictated by the bowl configuration.
It is, therefore, a principle object to this invention to provide an improved combustion chamber for a direct injected internal combustion engine wherein the compression ratio may be significantly raised without causing problems in clearance for the valves and while insuring rapid flame propagation and complete combustion under all running conditions.
It is a further object to this invention to provide an improved high efficiency combustion chamber, fuel injection and ignition arrangement for direct injected engines.
This invention is adapted to be embodied in an internal combustion engine that is comprised of an engine body that defines at least one cylinder bore that is closed at one end by a cylinder head surface and at the other end by the head of a piston that reciprocates in the cylinder bore. A fuel injector is mounted in the engine body contiguous to the axis of the cylinder bore. The fuel injector is configured to spray fuel downwardly toward the piston head and in at least two circumferentially spaced, fuel injection directions. The piston head is formed with a cavity arrangement having at least two circumferentially spaced, concave curved wall portions that curve upwardly toward the cylinder head at their radially outer extent. The circumferential spacing at the fuel injection directions correspond to the circumferential spacing of the piston concave curved wall portions so that fuel sprayed from the fuel injector is directed toward the piston concave curved wall portions. A pair of circumferentially spaced ignition devices are provided in the cylinder head surface in proximity to the upper ends of the piston concave curved wall portions for igniting the fuel sprayed from the fuel injector.